A magnetic disk recording system 11, shown in FIG. 1, includes a thin film magnetic transducer 20 and a disk 16 with magnetic thin films formed thereon. The disk 16 is rotated under the transducer 20 which writes and reads magnetic domains in ferromagnetic material on the disk. The read and write head portions of the transducer (also called a head or slider) are built-up in layers using thin film processing techniques. In the typical process of fabricating thin film magnetic heads, a large number of heads are formed simultaneously on a wafer. After the basic structures are formed the wafer is cut into rows or individual sliders. The exposed edges of the thin film are further processed to become the ABS of the slider. The protective overcoat which is normally formed over the slider components on the ABS is not shown. The magnetic sensor can be any one of various types including tunnel-junction (TMR) and spin valves (GMR). The magnetic transducer 20, shown in FIG. 1 is composed of elements that perform the task of writing magnetic transitions (the write head 21) and reading the magnetic transitions (the read head 22). The components of the read head 22 are the first shield (S1), the sensor element 25 and the second shield (S2). Separation layer 26 separates S2 from P1 and contributes to the spacing between the read head 22 and the write head 21. The yoke in the write head 21 includes three pole pieces P1 34, P2 32 and P3 43. P1 has a pedestal pole piece 34P. The P2 32 confronts the P1P 34P across the write gap layer 42 to form the write gap at the ABS. Typically write heads only have one coil layer 37, but two or more coil layers 37, 39 are possible. The P3 43 arches over the resist mound 44. Small tips (not shown) are formed on the pedestal and P2 to confront each other across the gap layer 42.
At various stages during the fabrication process chemical-mechanical polishing (CMP) is used to planarize the wafer, achieve desired thicknesses of features. For example, CMP is used to planarize the surfaces of S1, P1, P1P, and P2. Features are typically formed on the wafer by plating through photolithography masks and followed by deposition of refill material over the wafer. CMP is used to planarize the wafer after the refill deposition. The active components in magnetic heads are typically metals such as copper, NiFe, CoFe and CoNiFe. The refill material is typically alumina. The slurry used for CMP conventionally includes an abrasive such as silica or alumina, surfactants, corrosion inhibitors and etchants. Conventionally in preparation for planarization the material for a head component such as shield and pole pieces are deposited significantly thicker than the final target value. Similarly the refill material is also deposited significantly above the final. When the CMP is executed the excess material is removed.
FIG. 2 is a symbolic illustration of a section of a head 126 for perpendicular recording. The section is taken perpendicular to the ABS. This figure and the others included herein are not to scale, in part because the smaller components and spacings would be unclear. This design has a single coil 318. The yoke is composed of ferromagnetic pole pieces 331, 312, 316, 310. The trailing shield 328 can also be considered a pole piece. This design includes a pair of studs 326 shown in dotted lines, since they do not appear in the midline cross-section, but rather flank the pole tips as viewed from the ABS on the left and right and connect the first pole piece 331 to the trailing shield 328. The sensor is element 304. The nonmagnetic metal gap layer is 322. Element 320 is an insulator layer. An alternative perpendicular head design can include a pedestal (not shown). When a pedestal is included the studs are not used. The pedestal in this alternative will be substantially similar to the one shown in FIG. 1 for the longitudinal head.
With the increasing demand to reduce cost for manufacturing magnetic recording heads has correspondingly fueled the challenge to find new materials and innovative techniques aimed toward fabricating critical head structures with reduce number of process steps and achieve higher yields. One area of focus in the head design is the order in which the first coil and pedestal are fabricated. Although the role of the pedestal and its position in a longitudinal head is important in optimizing the write bubble, it is more flexible in perpendicular recording. Some single pole concept designs for perpendicular recording do not incorporate a pedestal. Recent evaluation of experimental single pole designs indicates corner writing of the return pole caused by flux saturation stemming from external fields and/or from the flux guide layer coupling to the soft-underlayer (SUL) and amplifying back to the return pole. Therefore, use of a pedestal into a perpendicular head design may provide improvements.
In current approaches the first coil can be fabricated before or after the pedestal. There can be two or more coils layers. The design in which a coil is fabricated before the pedestal will be called the “bionic” design and the design in which a pedestal is fabricated before the first coil will be called the planar design.
With the bionic design, the coil structure is fabricated on a CMP polished surface separated by an insulating gap and encapsulated with hard bake resist then the pedestal and back-gap structures are built 46, 47. The major advantage of this technique is that the coil is built on a lithographically favorable surface whereby resist uniformity and lithography scattering effects are tightly controlled to achieve excellent within wafer and wafer-to-wafer critical dimensions (CD) and overlay reproducibility. In addition, this approach offers a vehicle to scale the coil pitch towards smaller dimension. The major disadvantage at this process is it requires two bard bake steps: the first encapsulates the coil for pedestal and back-gap fabrication (E1) and the second encapsulates with additional hard bake to seal the hard bake within the pedestal and back-gap pocket (EF).
In the planar design, the pedestal and back-gap structure 47 are simultaneously fabricated by a through-mask plating approach and encapsulated with an insulator such as alumina followed by deposition of the coil seed-layer and subsequent coil fabrication. The coil seed layer is removed by ion milling and the coil structure is encapsulated with hard bake resist in the pedestal and back-gap pocket (E1). The major advantage or this technique is that it uses only one hard bake step. The major drawback to this technique as compared to the bionic design is that it requires the modification of the coil structure for higher pitch coil to compensate for the non-uniformity of the resist profile and attenuation of lithography light scattering effects due to the present of the pedestal and back-gap during coil fabrication. Although the benefit of this technique removes an additional hard bake step, it limits the extendibility of the coil process toward the narrow coil pitch which is needed.
In US patent application 2003/0174435 by Dinan, et al., a method for aligning a coil for an inductive head structure using a patterned seed layer is disclosed. The invention uses an alignment process where the base plate imprint is fabricated on an electrically insulating layer and the reversed image is fabricated and etched into the coil insulation material, e.g., hard bake photoresist to alleviate the problems associated with complete ion removal of the seed layer between high aspect ratio coils.
In US patent application 2004/0066576 by Lee, et al. a magnetic write head having a vertically laminated back gap structure is disclosed. The magnetic head is formed with lower and upper pole pieces and a back gap structure which connects the lower and the upper pole pieces in a back gap region. In one illustrative example, the back gap is a vertically laminated structure having alternating layers of magnetic and non-magnetic materials. Each alternating layer is perpendicular to both the lower and the upper pole pieces. This vertically laminated structure significantly reduces the eddy currents in the back gap region at high operating frequencies as the layers are oriented in a direction parallel with the magnetic flux.
In US patent application 20020191351 by Hugo Santini a method of making a magnetic write head includes forming a strip of negative photoresist on a wafer at an ABS site with a width that defines a track width of the write head and which has a height above a desired height of a second pole tip. An alumina layer is formed on the wafer and on the strip with a thickness above the wafer that is equal to or greater than a desired height of the second pole tip. The alumina layer is then mechanically polished until the negative photoresist strip is exposed. The negative photoresist strip is then removed leaving an opening in the alumina layer after which the second pole tip is formed in the opening. In a first embodiment of the invention the second pole tip and the second pole piece yoke are one piece and are planar and in a second embodiment of the invention a P2 yoke is stitched to the second pole tip. In both embodiments the first pole piece of the write head can be notched without damaging the second pole tip.
In US patent application 20020191349 by Hsu, et al., a magnetic head assembly includes first and second pole pieces and first and second coil layers. In a first embodiment the second pole piece structure is a single layer and in a second embodiment the second pole piece structure has front and back components with a flat laminated second pole piece yoke layer located there between. In addition to the first pole piece layer, the first pole piece of the write head includes a pedestal, which is located at and forms a portion of the ABS, and a back gap component which is located at the back gap. Between the pedestal and the back gap component is located a dielectric insulation layer which is located on the first pole piece layer. On the insulation layer is a first write coil layer which is also located between the pedestal and the back gap component. An insulation layer insulates the turns of the write coil from one another as well as insulating the write coil from the pedestal and the back gap component. In a preferred embodiment the insulation layer 207 includes a hard baked photoresist film 208 which insulates the write coil 206 between its turns and an alumina layer 210 which further insulates the write coil from the pedestal and the back gap component. At this stage the write head is planarized so that the pedestal, the back gap component, the write coil, the hard baked photoresist and the alumina layer form a first coplanar surface. The first coplanar surface has a middle region which is located between front and back gap regions. A write gap layer extends over the entire wafer except at the back gap component.